Enhancement Of Gas-liquid Mass Transfer Research Articles

Investigation into the Enhancement of Gas-Liquid Mass Transfer of Absorption of H2S by MDEA with Carbon Quantum Dots.

Although the addition of fine particles can enhance mass transfer, the stability of suspension is still a challenge. Responding to this, this study introduced carbon quantum dots (CQDs) with good hydrophilicity into a desulfurizer. N-doped carbon quantum dots (N-CQDs) were prepared by the hydrothermal method and characterized by TEM, FT-IR, and XPS. The stability and rheological properties of MDEA-based CQD solutions with different concentrations were studied. CQD solutions with low concentrations showed good stability, and the viscosity of CQD solutions was positively correlated with concentration and inversely correlated with temperature. The desulfurization experiment showed that the desulfurization effect and mass transfer enhancement of MDEA-based CQD solutions were coinfluenced by the viscosity and concentration of the solution; 0.01 vol % CQD solution had the best desulfurization effect, and the mass transfer coefficient was 0.66 mol/(m3h kPa), which increased by 26.61% compared to the base solution.

Process Intensification in Gas–Liquid Mass Transfer by Modification of Reactor Design: A Review

Process intensification is one way of developing new efficient production pathways for the chemical industry to overcome the increasing global energy demand and solve global energy and environmental problems. Process intensification plays an important role in the gas–liquid mass transfer processes. Herein, an overview of the development in gas–liquid mass transfer enhancement is provided. Classical mass transfer models such as two‐film theory, penetration theory, and surface renewal theory are analyzed. Major enhancement methods, namely, mechanical modification of reactor, are summarized and discussed here. The most recent accomplishments in gas–liquid mass transfer engineering are also provided. This review is expected to inspire new research on gas–liquid mass transfer engineering to enhance the future development and potential applications of gas–liquid mass transfer in scientific and industrial fields. Suggestions for the enhancement of gas–liquid mass transfer are also provided.

A new gas–liquid mass transfer enhancement method for a multi-downcomer sieve tray: Bubble breakup by falling droplets

Gas–liquid multiphase flows are a significant phenomenon in many chemical processes. Smaller bubbles have higher mass transfer efficiency, so this work proposes a new gas–liquid mass transfer enhancement method for a multi-downcomer sieve tray: bubble breakup by falling droplets. The motion of the bubbles was studied with computational fluid dynamics and particle image velocimetry. The main depth of influence of droplets was determined to be around 15 mm. A droplet breaks a bubble better when the gas velocity is 0.34–0.42 m/s. The droplet enters the liquid layer and acts directly or indirectly on the bubble, increasing its residence time and surface area after large bubbles impacted by droplets are split into smaller ones. The flow field around the bubble changes, the pressure and velocity inside the bubble increase, and the surface renewal accelerates. CO2 absorption experiments show that droplet-broken bubbles enhance the gas–liquid mass transfer effect.

Measurements of the effective mass transfer areas for the gas–liquid rotating packed bed

Rotating packed bed (RPB) is one of the most effective gas–liquid mass transfer enhancement reactors, its effective specific mass transfer area (ae) is critical to understand the mass transfer process. By using the NaOH–CO2 chemical absorption method, the ae values of three RPB reactors with different rotor sizes were measured under different operation conditions. The results showed that the high gravity factor and liquid flow rate were major affecting factors, while the gas flow rate exhibited minor influence. The radius of packing is the dominant equipment factor to affect ae value. The results indicated that the contact area depends on the dispersion of the liquid phase, thus the centrifugal force of rotating packed bed greatly influenced the ae value. Moreover, the measured ae/ap (effective specific mass transfer area/specific surface area of packing) values were fitted with dimensionless correlation formulas. The unified correlation formula with dimensionless bed size parameter can well predict the experimental data and the prediction errors were within 15%.

Enhancement of gas-liquid mass transfer and mixing in zigzag microreactor under ultrasonic oscillation

Ultrasonic oscillation can be leveraged to efficiently intensify the gas-liquid mass transfer in microreactors. This work aims at revealing the gas-liquid mass transfer enhancement mechanism in zigzag ultrasonic microreactors (zigzag USMRs). A rigorous and quantitative comparison of the O2 mass transfer performance and mixing efficiency inside the liquid slug during the Taylor bubbles flowing within the straight and zigzag USMRs was made. The synergetic effect of zigzag geometry and ultrasonic oscillation can enhance the mass transfer by an enhancement factor from 1.88 to 3.80. However, this synergetic effect would not have a significant impact on the mixing efficiency inside the liquid slug with an enhancement factor from 0.91 to 1.03. The synergetic enhancement effect of gas-liquid mass transfer performances could not be regarded as simply adding up the separate contribution of zigzag geometry and ultrasonic oscillation. Semi-empirical equations were established to predict the overall mass transfer coefficient in zigzag USMRs.

Enhancement of gas-liquid mass transfer in curved membrane contactors with the generation of dean vortices

The generation of Dean vortices in the membrane contactor is regarded as one of the critical technologies for gas-liquid mass transfer enhancement at low liquid Reynolds number. In this work, the gas-liquid mass transfer enhancement by Dean vortices in the curved hollow fiber membrane contactors is rapidly characterized based on the flux balance of gas across the membrane and dissolved in liquid. The effects of Reynolds number, curved diameter, liquid viscosity and rheology on the gas-liquid mass transfer enhancement with different curved shapes are systematically determined. The gas-liquid mass transfer correlations are proposed to describe the enhancement effect of Dean vortices on gas-liquid system with different viscosities. At the helical diameter of 6 mm and Reynolds number of 308, the enhancement factor is up to around 2.5. Furthermore, the trade-off relation between gas-liquid mass transfer intensification and energy consumption across the curved membrane contactors is investigated. The liquid velocity profile is also obtained by the finite element numerical simulation with COMSOL Multiphysics software to evaluate the Dean vortices intensity generated in different curved shapes, which agrees well with the experimental results.

Enhancement of gas-liquid mass transfer by nanofluids in a microchannel under Taylor flow regime

The gas-liquid two-phase flow and the enhancement of mass transfer by nanoparticles for the process of CO2 absorbed by SiO2 nanofluids were investigated in a microchannel under Taylor flow regime. The influences of the dispersed and continuous phase flow rates and particle concentration in slurry on liquid side volumetric mass transfer coefficient (KLa), mass transfer enhancement factor (E), CO2 absorption efficiency, and pressure drop were studied systematically. The results show that the presence of nanoparticles can effectively enhance the gas-liquid mass transfer. Both KLa and pressure drop increase, while the CO2 absorption efficiency decreases with increasing the gas-liquid flow rate ratio. Differently, KLa, CO2 absorption efficiency and pressure drop increase with the increase of particle concentration in slurry. Considering the energy consumption and mass transfer enhancement effect, the effective mass transfer enhancement efficiency is in the range of 1.2 ~ 2.4, which shows the excellent enhancement performance of nanoparticles on gas-liquid mass transfer.

Microscopic experimental study of nanoparticle motion for droplet evaporation enhancement in nanofluids

Adding nanoparticles to liquids to promote gas-liquid mass transfer has attracted attention in recent years. However, previous research mainly involved macroscopic experiments to determine the macroscopic behavior of nanoparticles to enhance absorption. In this paper, the microscopic state of the gas-liquid mass transfer of nanoparticles in the process of droplet evaporation is studied. The ability of nanoparticles to enhance mass transfer was measured and analyzed. Experimental results show that the concentration of nanoparticles gradually increases and becomes stable. In the initial stage of evaporation, the velocity of TiO2 nanoparticles caused by Brownian motion is 1.71 mm/s, but it decreases at 200 s, and then increases to 2.13 mm/s. The particle concentration at the gas-liquid mass transfer interface was initially very low, only 0.31 N/mm2 after 112 s, and gradually increased to 6.54 N/mm2 as the gas-liquid mass transfer progressed. The maximum enhancement factor E values of 60 nm and 100 nm TiO2 nanoparticles with a solid content of 0.4 g/L are 1.19 and 1.06, respectively. The effect of nanoparticles on the enhancement of deionized water droplet evaporation was determined to characterize the effect of nanoparticles on the enhancement of gas-liquid mass transfer.

Enhancement of gas-liquid mass transfer in microchannels by rectangular baffles

The configuration of microchannel with staggered rectangular baffles was constructed to improve the gas-liquid mass transfer efficiency. The influences of the baffle blockage length, baffle interval, channel width and the gas and liquid superficial velocities on the volumetric mass transfer coefficient, pressure drop and efficient energy efficiency for CO2/water system were investigated experimentally. The enhancement mechanism of mass transfer was analyzed according to the gas-liquid two-phase flow pattern in baffled microchannels. The comparison of the volumetric mass transfer coefficient between the microchannels with and without baffles was performed to present the intensification of baffled structure to mass transfer. The increases of baffle blockage length and channel width, and the reduction of baffle interval are conducive to enhancing gas-liquid mass transfer, with the maximum enhancement factor up to 2.8. Although the baffled structure could lead to an increase in pressure drop within 0.5 kPa in absolute value or 23% in relative value, which is an acceptable rise for practical application. Moreover, effective energy efficiency could reach to 2.25 in the case of the maximum enhancement of mass transfer. This study could provide theoretical guidance for the development and optimization of rectangular baffled microdevices for process intensification.

Wet scrubber coupled with heterogeneous UV/Fenton for enhanced VOCs oxidation over Fe/ZSM-5 catalyst

The traditional treatment processes for volatile organic compounds (VOCs) removal generally suffered several disadvantages, such as secondary air-pollutants. To overcome these issues, wet scrubber coupled with heterogeneous UV/Fenton was developed for gaseous VOCs (i.e. toluene) removal. ZSM-5 supported iron oxide (Fe/ZSM-5) was prepared as a multifunctional catalyst for activation of H2O2 and enhancement of gas-liquid mass transfer. Toluene was removed efficiently by this coupled process with the removal efficiency of 85% during 120 min. Many intermediates were detected in the solution by GC-MS while no intermediates were observed in the outlet gas, suggesting that wet scrubber coupled with heterogeneous UV/Fenton could significantly reduce secondary air pollutants. The possible mechanism of toluene oxidation was proposed including the physical adsorption by Fe/ZSM-5 and OH oxidation. This study provides an environmentally benign and highly efficient chemical scrubbing process for gaseous VOCs removal.

Enhancement effect and mechanism of gas-liquid mass transfer by baffles embedded in the microchannel

The enhancement of gas-liquid mass transfer by baffles embedded in a microchannel was investigated experimentally for CO2 absorption into monoethanolamine/1-butyl-3-methylimidazolium tetrafluoroborate (MEA/[Bmim][BF4]) aqueous solutions. The influences of baffle size on mass transfer rate and pressure drop were studied through varying the MEA/[Bmim][BF4] concentration ratio, gas-liquid flow rate and blockage ratio. Experimental results showed that the proper baffle configuration could improve effectively gas-liquid mass transfer performance. Although the pressure drop of the baffled microchannel has slight increase (the maximum growth 0.3 kPa, or 20% in relative term) in comparison with the unobstructed microchannel, it is acceptable for industrial application. Under lower MEA/[Bmim][BF4] concentration ratios, higher two-phase flow rates and blockage ratios, the mass transfer enhancement is more pronounced and the enhancement factor could reach to 1.5. A new empirical correlation of enhancement factor is proposed with good predictive performance.

Review of gas–liquid mass transfer enhancement by nanoparticles from macro to microscopic

Gas–liquid mass transfer is an extremely common process in the chemical industry and enhancing this process can help achieve high efficiency and low energy consumption. The addition of nanoparticles in the liquid phase is an important method for enhancing such transfers. In this paper, the preparation methods of nanofluids are briefly described and the parameters associated with nanofluid transport, such as mass-transfer coefficient, liquid volumetric mass-transfer coefficient, mass transfer interface area, and gas holdup, are introduced. Then, the latest experiments and mechanisms for the effect of nanofluids on the gas–liquid mass transfer process are reviewed from the viewpoint of transport parameters. The reasons for the enhancement of gas–liquid mass transfer by nanofluids are given: shuttle effect, mixing of the gas–liquid boundary layer, and inhibition of bubble coalescence. Finally, the problems existing in current research are assessed and, toward enhancing gas–liquid mass transfer using nanoparticles, future research directions are proffered.

Analysing the Operating Limits in High Gravity Equipment

The enhancement of gas-liquid mass transfer is one of the key challenges in chemical separation processes. So far, gas-liquid contacting is predominantly performed in counter-currently operated conventional columns. However, economic and environmental constraints require continuous process improvement in terms of separation efficiency and capacity. Therefore, new column internals have been developed for conventional columns allowing for increased throughput at high performance (Spiegel and Duss, 2014). A fundamentally different approach to increase the hydraulic capacity in contacting equipment is to superimpose the gravitational force by applying a centrifugal force.To realize this approach a ring shaped packing is mounted on a rotating shaft in a so-called rotating packed bed (RPB). By application of centrifugal forces, 10-1000 times higher than the gravitational force, a capacity increase is achieved. Although the increased throughput comes at the price of an elevated pressure drop and additional power consumption of the rotating equipment, it provides a great potential for debottlenecking of existing processes or implementing gas-liquid separation technologies in space limited environment and mobile environments, like off-shore applications. Furthermore, the rotational speed acts as an additional degree of freedom for an RPB, which provides additional flexibility in terms of applicable operational conditions. Besides the height of a packing and the specific packing material, recent studies by Neumann et al. have shown that also the type of nozzle for the distribution of the liquid in the eye of the rotor is of significant importance for the specific operating limits of an RPB. Therefore, the right choice of a nozzle design can facilitate a significant higher hydraulic capacity (Neumann et al., 2017a).In the present study, we investigate the operating limits with liquid loads, at the inner cross-sectional area, up to 320 m3m2h-1 and a F-factor of 4 Pa0.5. We provide detailed insights on the relationship between the pressure drop and the rotational speed and elucidate which rotational speed is needed to achieve a certain capacity for the equipment.

Modeling study of gas-liquid mass transfer enhancement by cylindrical catalyst particles

In this work, the influences of non-spherical catalyst particles on the enhancement of the gas-liquid mass transfer are numerically studied. The 3D unsteady diffusion-reaction equation both in the liquid phase and the solid catalyst particles is solved. A pseudo-homogenous model is employed as well. It is found that the SV cylindrical particles increase enhancement factor while SRSV cylindrical particles decrease it in comparison with the corresponding spherical particles. The horizontal cylinder and the vertical cylinder show small differences. The enhancement factor increases with catalyst concentration, rate coefficient of reaction and decreasing particle size. The data of pseudo-homogenous model agree well with the corresponding results of the fully resolved simulations.

Gas–liquid mass transfer enhancement by catalyst particles, a modelling study

In this paper we studied the effect of catalyst particles on the enhancement of the gas–liquid mass transfer due to a first order heterogeneously catalyzed reaction. The enhancement factor was obtained by solving the liquid side unsteady reaction-diffusion equation accounting for the presence of the particles. The results are compared with an analytical model that was derived assuming a homogeneous distribution of the particles in the liquid film. It was found that the enhancement factor increases with increasing catalyst concentration and increasing rate of reaction, as expected. As the particle diameter is increased, the enhancement factor decreases due to an increasing degree of diffusion limitation.The results of the homogeneous model match well with the results of the numerical simulations within a 10% error. Therefore it is concluded that the homogeneous model can be used to predict the enhancement of the mass transfer due to the presence of catalytic particles.

Mass transfer coefficient evaluation for pilot scale fermenter using sodium sulphite oxidation method

An adequate supply of oxygen in aqueous solution becomes the focal point of interest when it comes to the growth and maintenance of most aerobic microbial and tissue cultures used for biochemical and pharmaceutical production. Unfortunately, oxygen mass transfer to the growth medium serves as a major growth limiting factor owing to it’s low solubility in aqueous solutions. (Approximately 10 ppm at ambient temperature and pressure). The reaction rate is such that as oxygen enters the liquid phase, it is immediately consumed to oxidize the sulfite so that the rate of oxidation equals that of the oxygen transfer. Oxygen must at first be transferred from gas bulk through a series of steps onto the surfaces of cells before it can be utilized. Therefore the enhancement of gas-liquid mass transfer during aerobic cultures and fermentations is always put into priority. The present study involves using the ‘Central Composite Design’, a statistical technique to determine the parametric conditions for the optimum volumetric mass transfer coefficient in a pilot scale (40L) fermenter. The optimum volumetric mass transfer coefficient was found to lie outside the range of parameters studied and analytical expressions was obtained to predict the volumetric mass transfer coefficients for the parameter ranges studied using response surface methodology. The analytical expression was addressed to be significantly valid based on ANOVA results.

Enhancement of Gas-Liquid Mass Transfer with Unsteadily Forward-Reverse Rotating Multiple Delta Blade Impellers in an Unbaffled Agitated Vessel

Enhancement of Gas-Liquid Mass Transfer with Unsteadily Forward-Reverse Rotating Multiple Delta Blade Impellers in an Unbaffled Agitated Vessel

The mechanism model of gas–liquid mass transfer enhancement by fine catalyst particles

Abstract In order to present the enhancement of gas–liquid mass transfer by heterogeneous chemical reaction near interface, the mechanism model has been proposed to describe the mass transfer rate for a gas–liquid–solid system containing fine catalyst particles. The composite grid technique has been used to solve the model equations. With this model the effect of particle size, first-order reaction rate constant, distance of particle to gas–liquid interface and residence time of particle near gas–liquid interface on the mass transfer enhancement have been discussed. The particle–particle interaction and slurry apparent viscosity can be considered in the model. The experimental data have been used to verify the model, and the agreement has been found to be satisfied.

Mass transfer enhancement of gas absorption in oil-in-water systems: a review

A review is presented on the gas–liquid mass transfer enhancement due to the presence of a second dispersed liquid phase. An attempt has been made to describe the mass transfer characteristics in a gas–liquid–liquid system. The ability of an immiscible oil phase to influence the possible pathway for gas transfer from the gas phase to the aqueous phase and to affect the gas–liquid interface and the volumetric mass transfer coefficient k L a is considered. Though the mass transfer in series looks the most logical explanation, there are many gaps and contradictions in the reported results of k L a, preventing any definite conclusion being reached. An enhancement factor ( E), which quantifies the effect of the oil addition on the gas–liquid mass transfer, is defined. Experimental enhancement factors are reported and compared to the theoretical maximum attainable enhancement factor ( E max). Possible mechanisms (“bubble covering”, “shuttle effect” and “permeability effect”) involved in mass transfer enhancement are assessed in detail. The commonly used “shuttle effect” mechanism, whose model proposes a direct usable expression of the enhancement factor, underestimates the reported experimental enhancement factors by about 20%. However, to date, it is not possible to satisfactorily propose a unique theory explaining the influence of the presence of an immiscible oil on mass transfer enhancement. Moreover, the development of sophisticated models has not yet reached satisfactory levels. Recommendations have been made for future research.

Intensification of iron removal rate during oxygen leaching through gas-liquid mass-transfer enhancement

Intensification of iron removal rate during oxygen leaching through gas-liquid mass-transfer enhancement